In my earlier issued U.S. Pat. No. 4,435,690, issued on Mar. 6, 1984, a primary circuit breaker was disclosed which provided both primary and secondary current interruption for both extended overloads and fault currents. The circuit breaker was externally operable and resettable. The temperature sensing system was responsive to fault current in the primary winding and to increases in the temperature of the insulating oil due to overloads or incipient faults.